Saim Flexible Airline Tubing for Aquariums, Terrariums and Hydroponics, Airline Tubing 300-Foot Spool Great for all your aquarium airline needs Flexible tubing that resists kinking Made of PVC material, safe for fish and good for fresh or salt water environments Size measures about internal diameter: 4mm/0.16"; outside diameter: 6mm/0.24". Notice: Due to different manufacture reason, the spool package could be slightly different from the picture.We GUARANTEE the airline tubing.quality is the same.PLEASE MAKE SURE YOU REALISE THIS BEFORE PLACE ORDER.